<template>
  <scroll
   :data="infos"
   class="listview"
   ref="listview"
   :listen-scroll="listenScroll"
   :probe-type="probeType"
   @scroll="scroll"
  >
    <ul>
      <li v-for="(group,index) in infos" :key="index" class="list-group" ref="listGroup">
        <h2 class="list-group-title">{{group.title}}</h2>
        <ul>
          <li v-for="(item,index) in group.list" :key="index" class="list-group-item"
          @click="onItemClick(item)"

          >
            <img class="avatar" v-lazy="item.pic">
            <span class="name">{{item.name}}</span>
          </li>
        </ul>
      </li>
    </ul>
    <div class="list-shortcut"
         @touchstart.stop.prevent="onShortcutTouchStart"
         @touchmove.stop.prevent="onShortcutTouchMove"
         @touchend.stop
    >
      <ul>
        <li v-for="(item,index) in shortcutList"
            :class="{'current': currentIndex === index}"
            :data-index="index"
            :key="index"
            class="item">
          {{item}}
        </li>
      </ul>
    </div>

    <div class="list-fixed" ref="fixed" v-show="fixedTitle">
      <div class="fixed-title">{{fixedTitle}}</div>
    </div>


    <div v-show="!infos.length" class="loading-container">
      <loading></loading>
    </div>
  </scroll>
</template>

<script>
import Loading from '@/base/loading/loading'
import Scroll from "@/base/scroll/scroll";
import {getData} from '@/common/js/dom'
const ANCHOR_HEIGHT = 18

export default {
  props:{
    infos: {
      type: Array,
      default () {
        return []
      }
    }
  },

  data(){
    return {
      currentIndex: 0,
      diff: -1,
      scrollY: -1

    }
  },
  watch: {
    infos(){
      setTimeout(() =>{
        this._calculateHeight()
      },20)
    },
    scrollY(newY) {
      const listHeight = this.listHeight
      //在顶部滑动
      if (newY > 0) {
        this.currentIndex = 0
        return
      }
      // 当滚动到底部，且-newY大于最后一个元素的上限
      this.currentIndex = listHeight.length - 2
      //滑动在中间
      for (let i = 0; i<listHeight.length-1;i++){
        let height1 = listHeight[i]
        let height2 = listHeight[i + 1]
        if (-newY >= height1 && -newY <=height2){
          this.currentIndex = i
          this.diff = height2 + newY
          return
        }
      }
    },
    diff(newVal){


    }
  },
  name: "listview",
  components: {
    Scroll,
    Loading
  },
  computed: {
    shortcutList() {
      return this.infos.map((group) =>{
          return group.title.substr(0,1)
      })
    },
    fixedTitle (){
      if (this.scrollY >0){
        return ''
      }
      return this.infos[this.currentIndex] ? this.infos[this.currentIndex].title : ''
    }
  },
  created() {
    this.probeType = 3
    this.listenScroll = true
    this.touch = {}
    this.listHeight = []
  },
  methods:{
    onItemClick(item) {
      this.$emit('select', item)
    },

    onShortcutTouchStart (e) {
      let anchorIndex = getData(e.target,'index');
      let firstTouch = e.touches[0]
      this.touch.y1 =  firstTouch.pageY
      //anchorIndex 就是定义的属性值
      this.touch.anchorIndex = anchorIndex
      this._scrollTo(anchorIndex)
    },
    onShortcutTouchMove(e) {
      let firstTouch = e.touches[0]
      this.touch.y2 = firstTouch.pageY
      let delta = (this.touch.y2 - this.touch.y1) / ANCHOR_HEIGHT | 0
      let anchorIndex = parseInt(this.touch.anchorIndex) + delta
      this._scrollTo(anchorIndex)

    },
    scroll (pos){
      this.scrollY = pos.y
    },
    _scrollTo(index) {

      if (!index && index != 0){
        return
      }
      if (index < 0) {
        index = 0
      } else if (index > this.listHeight.length - 2){
        index = this.listHeight.length - 2
      }
      this.$refs.listview.scrollToElement(this.$refs.listGroup[index], 0)

    },
    _calculateHeight(){

      this.listHeight = []
      const list = this.$refs.listGroup
      let height = 0
      this.listHeight.push(height)
      for (let i=0;i<list.length;i++){
        height +=  list[i].clientHeight
        this.listHeight.push(height)
      }
    }

  }

}
</script>

<style scoped lang="stylus">
@import "~common/stylus/variable"

 .listview
   position relative
   width 100%
   height 100%
   overflow hidden
   background: $color-background
   .list-group
     padding-bottom: 30px
     .list-group-title
       height: 30px
       line-height: 30px
       padding-left: 20px
       font-size: $font-size-small
       color: $color-text-l
       background: $color-highlight-background
     .list-group-item
       display flex
       padding: 20px 0 0 30px
       align-items center
       .avatar
         width: 50px
         height: 50px
         border-radius: 50%
       .name
         margin-left: 20px
         color: $color-text-l
         font-size: $font-size-medium
   .list-shortcut
     position absolute
     right 0
     top 50%
     transform: translateY(-50%)
     width 20px
     padding 20px 0
     border-radius: 10px
     text-align: center
     background: $color-background-d
     .item
       padding: 3px
       line-height: 1
       color: $color-text-l
       font-size: $font-size-small
       &.current
         color: $color-theme
  .list-fixed
   position: absolute
   top: 0
   left: 0
   width: 100%
   .fixed-title
     height: 30px
     line-height: 30px
     padding-left: 20px
     font-size: $font-size-small
     color: $color-text-l
     background: $color-highlight-background
   .loading-container
     position absolute
     width 100%
     top 50%
     transform: translateY(-50%)
</style>
